CN1402885A - Intersystem crossing agents for efficient utilization of excitons in organic light emitting device - Google Patents

Abstract

Organic light emitting devices are described wherein the emissive layer comprises a host material containing a fluorescent or phosphorescent emissive molecule, which molecule is adapted to luminesce when a voltage is applied across the heterostructure, wherein an intersystem crossing molecule of optical absorption spectrum matched to the emission spectrum of the emissive molecule enhances emission efficiency.

Description

Intersystem transition agent for efficient utilization of excitons in organic light-emitting devices

I. Field of the Invention

The present invention relates to organic light emitting devices (OLEDs) consisting of an emissive layer containing an organic compound as emitter and a separate intersystem transition ("ISC") entity for enhancing emission efficiency.

II. Background of the Invention

II.A. General background

An organic light-emitting device (OLED) is composed of several organic layers, one of which is composed of an organic material that induces electroluminescence by applying a voltage to the device, C.W.Tang et al., Appl.Phys.Lett.1987, 51 , 913. Certain OLEDs have been shown to have sufficient brightness, color gamut, and operating lifetime for use as practical replacement technologies for LCD-type full-color flat panel displays (S.R. Forrest, P.E. Burrows and M.E. Thompson, Laser Focus World, February 1995). Since many of the thin organic films used in these devices are transparent in the visible spectral region, they enable entirely new types of display pixels in which red (R), green (G) and blue (B) light-emitting OLEDs are arranged in vertically stacked geometry to provide simple fabrication process, small R-G-B pixel size, and large fill factor, International Patent Application No. PCT/U595/15790.

Representing a significant advance towards realizing high-resolution, individually addressable stacked R-G-B pixels, transparent OLEDs (TOLEDs) have been reported in International Patent Application No. PCT/US97/02681, where the TOLEDs are Has greater than 71% transparency and emits light from the upper and lower device surfaces with high efficiency (close to 1% quantum efficiency) when the device is turned on. The TOLED uses transparent indium tin oxide (ITO) as a hole injection electrode and a Mg-Ag-ITO electrode layer for electron injection. A device is disclosed in which the ITO side of the Mg-Ag-ITO electrode layer is used as a hole injection contact layer to stack a second, differently colored, light-emitting OLED on top of the TOLED. Each layer in a stacked OLED (SOLED) is independently addressable and emits its own characteristic color. This colored emission is able to pass through adjacent stacked, transparent, individually addressable organic layers, transparent contact layers, and glass substrates, thus allowing devices to emit light of any color by changing the red and The relative output power of the blue light-emitting layer is generated.

PCT/US95/15790 patent application discloses integrated SOLEDs that can independently vary and control light intensity and color with an external power source in a color-tunable display device. Patent application PCT/US95/15790 thus demonstrates the principle of obtaining integrated, full-color pixels to provide high image definition (made possible by the fine pixel size). Furthermore, lower cost fabrication techniques may be used to fabricate such devices in close proximity to prior art methods.

II.B. Background of illuminants

II.B.1. Basic information

I1.B.1.a. Singlet and triplet excitons

Because light is produced by the decay of excited states of molecules or excitons in organic materials, it is understood that their properties and interactions are of great importance to the The design of efficient light emitting devices is very critical. For example, if the symmetry of the excitons is different from that of the ground state, the radiative relaxation of the excitons is prevented and light emission is slow and inefficient. Because the ground state is usually antisymmetric under the exchange of spins of electrons including excitons, the decay of symmetric excitons breaks the symmetry. Such excitons are known as triplets, a term that reflects how degenerate the state is. For every three triplet excitons formed by electrical excitation in OLEDs, only one symmetric (or singlet) exciton is generated. (M.A. Baldo, D.F.O'Brien, M.E. Thompson and S.R. Forrest, Extremely efficient green organic light-emitting devices based on electroluminescence phosphorescence, Applied Physics Letters, 1999, 75, 4-6). Luminescence from symmetry-forbidden processes is known as phosphorescence. Characteristically, phosphorescence can persist for at most several seconds after excitation, which is attributed to the low probability of transition. Instead, fluorescence occurs in the rapid decay of singlet excitons. Because this process occurs between states that resemble symmetry, it is very efficient.

Many organic materials exhibit the ability to fluoresce from singlet excitons. However, only a few have been identified, which also enable efficient room-temperature phosphorescence from the triplet state. Therefore, in most fluorescent dyes, the energy contained in the triplet state is wasted. However, efficient phosphorescence is more likely if this triplet excited state is disturbed, for example, by spin-orbit coupling (typically caused by the presence of heavy metal atoms). In this case, the triplet excitons exhibit some singlet characteristics and have a high probability of radiative decay to the ground state. Indeed, phosphorescent dyes with these properties have been shown to function with high efficiency electroluminescence.

Only a few organic materials have been confirmed to display efficient room-temperature phosphorescence from the triplet state. On the contrary, many fluorescent dyes are known (C.H.Chen, J.Shi.and C.W.Tang, "Recent developments inmolecular organic electroluminescent materials (Recent developments inmolecular organic electroluminescent materials)", Macromolecular Symposia, 1997, 125, 1- 48; U.Brackmann, Lambdachrome Laser Dyes (Lambda Physik, Gottingen, 1997) and the situation that the fluorescence efficiency in solution is close to 100% is not common. (C.H.Chen, 1997, op, cit). Fluorescence is not affected by triple state-triplet annihilation, which reduces phosphorescent emission at high excitation densities. (M.A.Baldo et al., "High efficiency phosphorescent emission from organic electroluminescent devices), Nature, 1998 , 395, 151-154; M.A.Baldo, M.E.Thompson, and S.R.Forrest, "Analytical Model of Triplet-Triplet Annihilation in Electroluminescent Phosphorescent Devices", 1999). Therefore, fluorescent substances are suitable for many electroluminescent applications, especially passive matrix displays.

II.B.1.b. Summary of the invention in relation to the basic situation

The present invention relates to the use of intersystem transition agents to enhance the emission efficiency in organic light-emitting devices. Intersystem transition agents or molecules are substances capable of intersystem transitions, which involve the transfer of populations between states of different spin multiplicity. A list of known intersystem transition agents or molecules is listed in A. Gilbert and J. Baggott, Essentials of Molecular Photochemistry, Blackwells Scientific, 1991 .

In one embodiment of the present invention, the inventors have focused on the use of intersystem transition agents to increase efficiency in systems with fluorescent emitters. Here the inventors describe a technique in which the triplet state formed in the host material is not wasted but transferred to the singlet excited state of the fluorescent dye. Utilizing all excited states and fluorescence in this way increases the overall efficiency by a factor of four. In this embodiment, the ISC agent captures the energy of the excitons and transfers the energy to the fluorescing emitter using the Forster energy transfer principle. The required energy transfer process is:

³ D*+ ¹ A→ ¹ D+ ¹ A*(Eq.1)

Here, D and A represent the donor molecule and the fluorescent acceptor, respectively. The superscripts 3 and 1 denote triplet and singlet states, respectively, and asterisks denote excited states.

In a second embodiment of the present invention, the inventors have addressed the use of intersystem transition agents to increase the efficiency in systems with phosphorescent emitters. Here the inventors describe a technique in which an ISC agent is responsible for converting all excitons from a host material to their triplet state and then transferring this excited state into a phosphorescent emitter. This includes situations where the ISC agent only captures singlet excitons on the host, and the host triplet excitons are transferred directly into the phosphorescent emitter (rather than via the ISC agent.)

In this second embodiment where phosphorescent efficiency is enhanced, phosphorescent emitters are used in combination with intersystem transition agents to enable the following to occur:

¹ D*+ ¹ X→ ¹ D+ ¹ X*

¹ X* → ³ X*

³ X*+ ¹ A→ ¹ X+ ³ A*

³ A*→ ¹ A+hv

where D denotes a donor (host), X denotes an intersystem transition agent, and A denotes an acceptor (emitted molecule). Superscript 1 indicates singlet spin multiplicity; superscript 3 indicates triplet spin multiplicity and the asterisk indicates an excited state.

In a third embodiment of the present invention, the inventors have focused on using intersystem transition agents as filters and converters to increase efficiency. In one aspect of the filter/converter embodiment, the intersystem transition agent is used to convert singlet excitons to triplet excitons, thereby keeping singlet states out of reach of the emissive region and thus enhancing optical purity ("filter" aspect: the singlet is removed and thus no singlet emission) and increased efficiency ("transition" aspect: the singlet is transformed into a triplet, which emits).

These embodiments are discussed in more detail in the Examples below. However, these embodiments may operate by different mechanisms. Without wishing to limit the scope of the invention, the inventors discuss different mechanisms.

II.B.1.c. Dexter and Forster Mechanism

Understanding the various embodiments of the invention facilitates a discussion of the basic mechanistic theory of energy transfer. Two mechanisms are generally discussed for energy transfer to acceptor molecules. In the first mechanism supported by Dexter (D.L. Dexter, "Theory of sensitized luminescence in solids", J. Chem. Phys., 1953, 21, 836-850), the excitons jump directly from one molecule to another molecular. This is a short-term approach that relies on the overlap of the molecular orbitals of adjacent molecules. It also preserves the symmetry of the donor and acceptor pair (E.Wigner and E.W.Wittmer, Uber dieStruktur der zweiatomigen Molekelspektren nach derQuantenmechanik, Zeitschrift fur Physik, 1928, 51, 859-886; M.Klessinger and J.Michl, Organic Molecules Excited state and photochemistry (VCHPublishers, New York, 1995). Therefore, the energy transfer of Eq. (1) is impossible for utilizing the Dexter mechanism. In the second mechanism of Forster transfer (T.Forster, Zwischenmolekulare Energiewanderung and Fluoreszenz, Annalen der Physik, 1948.2, 55-75; T.Forster, Fluoreszenzorganischer Verbindugen (Vandenhoek and Ruprecht, Gottinghen, 1951), the energy transfer of Eq.(1) is possible. In the Forster transfer, similar to the transmitter and antennae, the dipoles on the donor and acceptor molecules will couple and energy can be transferred. Dipoles are generated from allowed transitions in the donor and acceptor molecules. This typically limits the singlet Between the Forster mechanism.

However, in one embodiment of the present invention, the inventors need to consider the case where the transition ( ^{3D *} → ^1D ) on the donor is allowed, ie the donor is a phosphorescent molecule. As already discussed, the probability of this transition is low because of the symmetric difference between the excited triplet state and the ground state singlet state.

Nevertheless, as long as the phosphor is able to emit light due to some perturbation of state such as spin-orbit coupling caused by heavy metal atoms, it participates in Forster transfer as a donor. The efficiency of this method is determined by the luminous efficiency of the phosphor (F Wilkinson, in Advances in Photochemistry (W.A.Noyes, G.Hammond and J.N.Pitts edited, pp.241-268, John Wiley & Sons, New York, 1964), namely Energy transfer is efficient if radiative transitions are more likely than nonradiative decay. This triplet-singlet transfer was predicted by Forster (T. Forster, "Transfer Mechanisms for Electron Excitation", Discussion of the Faraday Society (Discussions of the Faraday Society), 1959, 27, 7-17) and confirmed by Ermolaev and Sveshnikova (V.L.Ermolaev and E.B.Sveshnikova, "Inductive-resonance transfer of energy from triplet aromatic hydrocarbon molecules of energy from aromaticmolecules in the triplet state)", Doklady Akademii Nauk SSSR, 1963, 149, 1295-1298), they used some phosphorescent donors and fluorescent acceptors to detect energy transfer at 77K or 90K in a rigid medium. It was observed that Large transfer distance: For example, for triphenylamine as donor and chrysoidine as acceptor, the interaction range is 52 Angstroms.

The remaining condition for the Forster transition is that, provided that the energy levels between the excited and ground state molecular pair are in resonance, the absorption spectrum should overlap the emission spectrum of the donor. In Example 1 of the present application, the inventors used a green phosphor, i.e., tris(2-phenylpyridine) iridium (Ir(ppy) ₃ ; MA Baldo et al., Appl.Phys.Lett., 1999, 75, 4- 6) and the red fluorescent dye [2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinazin-9-yl)vinyl]-4H -pyran-ylidene]propane-dinitrile] ("DCM2"; CW Tang, SAVanSlyke and CH Chen, "Electroluminescence of Doped Organic Films", J.Appl.Phys., 1989, 65, 3610-3616) . DCM2 absorbs in the green region and depends on the local polarization field (V. Bulovic et al., "Bright, saturated, red-to-yellow organic light-emitting devices based on polarization-induced spectral shifts", Chem. Phys. Lett., 1998, 287, 455460), which emits at wavelengths between λ=570 nm and λ=650 nm.

It is also possible to perform Forster energy transfer from the triplet state by doping fluorescent guests into phosphorescent host materials. Unfortunately, such systems suffer from competing energy transfer mechanisms that reduce overall efficiency. In particular, the proximity of host and guest increases the likelihood of Dexter transfer between host-to-guest triplets. Once the excitons reach the guest triplet state, they are effectively lost since these fluorescent dyes typically exhibit extremely inefficient phosphorescence.

Another approach is to simultaneously dope a phosphorescent donor and a fluorescent acceptor into the host material. This energy can cascade from the host, through the phosphor sensitizing molecule and to the fluorescent dye, according to the following set of equations (collectively Eq. 2):

³ D*+ ¹ X→ ¹ D+ ³ X*

³ X*+ ¹ A→ ¹ X+ ¹ A*

¹ A*→ ¹ A+hv (2a)

¹ D*+ ¹ X→ ¹ D+ ¹ X*

¹ X* → ³ X*

³ X*+ ¹ A→ ¹ X+ ¹ A*

¹ A*→ ¹ A+hv (2b)

where X represents the sensitizer molecule and hv is the photon energy.

The multi-state energy transfer required in a phosphorescently sensitized system is schematically depicted in FIG. 1 . Dexter metastases are indicated by dotted arrows, and Forster metastases by solid arrows. Shifts that result in a loss of efficiency are marked with a cross. In addition to the energy transfer pathways shown in the figure, direct electron-hole recombination is possible for phosphorescent and fluorescent dopants and hosts. Triplet exciton formation following charge recombination on the fluorochrome is another potential loss mechanism.

In order to maximize transfer from the host triplet state to the fluorochrome singlet state, it is desirable to maximize Dexter transfer to the phosphor triplet state while minimizing transfer to the fluorochrome triplet state. Because the Dexter mechanism transfers energy between adjacent molecules, reducing the concentration of a fluorescent dye will reduce the probability of triplet-triplet transfer to that dye. On the other hand, the long-distance Forster transition to the singlet state was not affected. In contrast, transfer to the triplet state of the phosphor is required to harness the host triplet state and can be improved by increasing the concentration of the phosphor. To demonstrate this multi-state transition, the inventors used 4,4'-N,N'-dicarbazole-biphenyl ("CBP") as the host (DFO*Brien, MA Baldo, METhompson and SRForrest, "In Electron Improved energy transfer in phosphorescent devices (Improved energy transfer in electrophosphorescent devices), Appl.Phys.Lett., 1999, 74, 442-444), Ir(ppy) ₃ as a phosphorescent sensitizer, and DCM2 as Fluorescent dyes. The doping concentration is 10% for Ir(ppy) ₃ and 1% for DCM2.

The details given in Example 1 below demonstrate the improvement in fluorescence efficiency brought about by the use of phosphorescent sensitizers. In the following sections, the inventors give additional background.

II.B.2. Interrelationship of Device Structure and Emission

Such devices, whose structure is based on the use of layers of organic optoelectronic materials, generally rely on common mechanisms leading to light emission. Typically, this mechanism is based on radiative recombination of trapped charges. Specifically, OLEDs consist of at least two thin organic layers that separate the anode and cathode of the device. The material of one of these layers is deliberately chosen based on the material's ability to transport holes, the "hole transport layer" (HTL), and the material of the other layer is deliberately chosen based on the material's ability to transport electrons, "Electron Transport Layer" (ETL). With such a configuration, when the potential applied to the anode is higher than the potential applied to the cathode, the device can be considered as a diode with a forward bias. Under these bias conditions, the anode injects holes (positive charge carriers) into the hole transport layer and the cathode injects electrons into the electron transport layer. The part of the luminescent medium adjoining the anode thus forms a hole injection and transport zone, while the part of the luminescent medium adjoining the cathode forms an electron injection and transport zone. The injected holes and electrons each migrate toward oppositely charged electrodes. A Frenkel exciton is formed when an electron and a hole are located on the same molecule. The recombination of this short-lived state can be conceived as an electron falling from its conduction potential to the valence band under certain conditions, preferably via a photoemission mechanism, with simultaneous relaxation. In this view of the working principles of typical thin-layer organic devices, the electroluminescent layer comprises a light-emitting region that accepts flowing charge carriers (electrons and holes) from each electrode.

As noted above, light emission from OLEDs is typically via fluorescence or phosphorescence. Various problems are encountered with the use of phosphorescence. It has been pointed out that the phosphorescence efficiency drops rapidly at high current densities. It is possible that the long phosphorescence duration causes saturation of the emission sites, and triplet-triplet annihilation may also lead to loss of efficiency. Another difference between fluorescence and phosphorescence is that the energy transfer of the triplet state from the conductive host to the luminescent guest molecule is typically lower than that of the singlet state; long-distance dipoles dominate the energy transfer of the singlet state - Dipole coupling (Forster transfer), forbidden (in theory) for triplets due to the principle of conservation of spin symmetry. Thus, for the triplet state, energy transfer typically occurs by exciton diffusion to neighboring molecules (Dexter transfer); sufficient overlap of donor and acceptor exciton wavefunctions is critical for energy transfer. Another problem is that triplet diffusion lengths are typically long (eg, >1400 Angstroms), compared to typical singlet diffusion lengths of about 200 Angstroms. Therefore, if phosphorescent devices are to realize their potential, the device structure needs to be optimized for triplet properties. In the present invention, the inventors utilized the property of long triplet diffusion length to improve external quantum efficiency.

The successful utilization of phosphorescence has great application prospects for organic electroluminescent devices. For example, the advantage of phosphorescence is that all excitons (formed by the recombination of holes and electrons in the EL), which are the (partial) triplet type in phosphorescent devices, can participate in energy transfer in certain electroluminescent materials and glow. In contrast, only a small percentage of excitons (of the singlet type) in fluorescent devices results in fluorescent luminescence.

An alternative is to use phosphorescent methods to improve the efficiency of fluorescent methods. In principle, the efficiency of fluorescence is 75% lower due to more than three times the number of symmetric excited states. In one embodiment of the present invention, the inventors overcome this problem by using phosphorescent sensitizing molecules to excite fluorescent species in red-emitting OLEDs. The mechanism of energy coupling between molecular entities is long-distance, non-radiative energy transfer from the phosphor to the fluorochrome. By using this technique, the internal efficiency of fluorescence can be as high as 100%, a result previously possible only with phosphorescence. As shown in Example 1, the inventors used it with almost four times the efficiency of fluorescent OLEDs.

II.C. Background of matter

II.C.1. Basic hybrid structures

Since there is typically at least one electron-transporting layer and at least one hole-transporting layer, the layers then have different substances, forming a hybrid structure. The material that produces this light emission of electroluminescence may be the same as that used as the electron transport layer or as the hole transport layer. Such devices in which the electron-transporting layer or the hole-transporting layer are also used as light-emitting layers are referred to as single heterostructures. In addition, the electroluminescent material may be present in a separate light-emitting layer between the hole-transport layer and the electron-transport layer, which is called a double hybrid structure. The separate emissive layer may contain emissive molecules doped into the host or the emissive layer may consist essentially of emissive molecules.

That is, in addition to the emission material that exists as a main component in the charge carrier layer, that is, in the hole transport layer or in the electron transport layer and serves as both the charge carrier material and the emission material, the emission material It can also be present in a lower concentration as a dopant in the charge carrier layer. Whenever a dopant is present, the predominant material in the charge carrier layer can be referred to as a host compound or as an acceptor compound. The material present as host and dopant should be selected such that it has a high level of energy transfer from the host to the dopant material. In addition, these materials need to be able to produce acceptable electrical properties for OLEDs. Furthermore, the host and dopant materials are preferably capable of being introduced into the OLED by using materials which can be easily introduced into the OLED by using convenient manufacturing techniques, especially by using vacuum deposition techniques.

I1.C.2. Exciton sealing layer

The exciton confinement layer used in the device of the present invention (and previously disclosed in US Application Serial No. 09/154.044) substantially blocks the diffusion of excitons, thus substantially keeping the excitons in the reflective layer to enhance device efficiency. The substance of the confinement layer of the present invention is characterized by the energy difference ("bandgap") between its lowest unoccupied molecular orbital (LUMO) and its highest occupied molecular orbital (HOMO). According to the invention, this energy band gap substantially prevents the diffusion of excitons throughout the confinement layer and has only a minimal influence on the turn-on voltage of the complete electroluminescent device. This energy bandgap is therefore preferably greater than the energy level of the excitons generated in the emissive layer, so that such excitons cannot be present in the confinement layer. Specifically, the energy bandgap of the sealing layer is at least as large as the energy difference between the triplet state and the ground state of the host.

For the case of a blocking layer between the hole-conducting host and the electron-transporting layer (as in Example 1 below), the following properties were sought, listed in order of relative importance.

1. The energy difference between the LUMO and HOMO of the sealing layer is greater than the energy difference between the triplet state and the ground state singlet state of the host material.

2. The triplet state in the host material is not quenched by the capping layer.

3. The ionization potential (ionization potential) of the sealing layer is greater than that of the host. (meaning the hole remains in the host.)

4. The energy level of the LUMO of the capping layer and the energy level of the LUMO of the host are sufficiently close in energy that there is less than a 50% change in the overall conductivity of the device.

5. The capping layer should be as thin as possible, but thick enough to effectively block the transport of excitons from the emissive layer to the adjacent layer.

That is, in order to seal excitons and holes, the ionization potential of the sealing layer should be greater than that of HTL, and the electron affinity of the sealing layer should be roughly equal to that of ETL, so that electrons can be transported relatively easily.

[For cases where emissive ("emitting") molecules are used without a hole-transporting host, the above rules for the choice of blocking layer may be modified by the word "emitting molecule" in place of "host". ]

For the complementary case of a capping layer between an electron-conducting host and a hole-transporting layer, the following properties (listed in order of importance) may be sought:

1. The energy difference between the LUMO and HOMO of the sealing layer is greater than the energy difference between the triplet state and the ground state singlet state of the host material.

2. The triplet state in the host material is not quenched by the capping layer.

3. The energy of the LUMO of the sealing layer is greater than the energy of the LUMO of the (electron transport) host. (Meaning that the electrons remain in the host.)

4. The ionization potential of the capping layer and the host should be such that holes are easily injected from the capping agent into the host with less than a 50% change in the overall conductivity of the device.

5. The capping layer should be as thin as possible, but thick enough to effectively block the transport of excitons from the emissive layer to the adjacent layer.

[For cases where an emissive ("emitting") molecule is used without an electron-transporting host, the above rules for the choice of capping layer may be modified by replacing "host" with the word "emitting molecule". ]

II.D. color

As for color, it is desirable to fabricate OLEDs using substances that provide electroluminescent emission in a narrower band centered around a selected spectral region corresponding to one of the three primary colors (red, green and blue). different colors so that the substance can be used as a colored layer in OLEDs or SOLEDs. It is also desirable that such compounds can be easily deposited as thin layers using vacuum deposition techniques so that they can be easily incorporated into OLEDs, which are produced entirely from vacuum deposited organic materials.

Pending US 08/774,333 (December 23, 1996) relates to OLEDs containing those light-emitting compounds that produce saturated red light emission.

III. SUMMARY OF THE INVENTION

On the most general level, the present invention relates to an organic light-emitting device comprising an emissive layer, wherein the emissive layer emissive molecules, for the host material (wherein the emissive molecules are provided as dopants in the host material) when along the heterogeneous The molecule emits light when a voltage is applied to an organic structure, wherein the emissive molecule is selected from phosphorescent or fluorescent organic molecules and wherein the device includes molecules that can act as intersystem transition agents ("ISC molecules") that improve phosphorescence or Efficiency of fluorescence, relative to the absence of ISC molecules. It is preferred that the emissive molecule and the intersystem transition molecule are different, and there is preferably sufficient spectral overlap between the emissive molecule and the intersystem transition molecule.

In a first embodiment in which the efficiency of fluorescence is enhanced, a fluorescent emitter is used in combination with a phosphorescent sensitizer, which acts as an intersystem transition agent. The phosphorescent sensitizer may be selected from those substances in which the rate of radiative recombination is much greater than the rate of non-radiative recombination. The phosphorescent sensitizer may be selected from cyclometallated organometallic compounds. Its metal can be selected from the metals of the third row of the periodic table (especially tungsten, platinum, gold, iridium, osmium) and any other metal or metal compound with strong spin-orbit coupling. The phosphorescent sensitizer is further selected from phosphorescent organometallic iridium or osmium complexes and still further from phosphorescent cyclometalated iridium or osmium complexes. A specific example of a sensitizer molecule is fac tris(2-phenylpyridine)iridium having the formula (Ir(ppy) ₃ ):

[In this and subsequent figures, the inventors have depicted the coordinate bond from nitrogen to the metal (here Ir) as a straight line. )

A specific example of a fluorescent emitter is DCM2 having the formula

In a second embodiment where the efficiency of phosphorescence is enhanced, the phosphorescent emitter is used in combination with an intersystem transition agent to enable the following to occur:

¹ D*+ ¹ X→ ¹ D+ ¹ X*

¹ X* → ³ X*

³ X*+ ¹ A→ ¹ X+ ³ A*

³ A*→ ¹ A+hv

where D denotes a donor (host), X denotes an intersystem transition agent, and A denotes an acceptor (emitted molecule). Superscript 1 indicates singlet spin multiplicity; superscript 3 indicates triplet spin multiplicity and the asterisk indicates excited states.

In a third embodiment of the invention, a thin layer of ISC agent is placed in the device; it may be between the HTL and the ETL. The ISC agent is chosen such that the optical absorption spectrum of the ISC agent strongly overlaps the emission line of the species found at the site of recombination.

The general arrangement of the hybrid structure of the device should be such that the order of the layers is the hole transport layer, the emissive layer, and the electron transport layer. For an emissive layer that conducts holes, it is possible to have an exciton-blocking layer between the emissive layer and the electron-transport layer. For an emissive layer that conducts electrons, it is possible to have an exciton-blocking layer between the emissive layer and the hole-transport layer. The emissive layer can be equal to the hole transport layer (in which case the exciton sealing layer is close to or on the anode) or equal to the electron transport layer (in which case the exciton sealing layer is close to or on the cathode on the cathode).

The emissive layer can be formed with a host material in which the emitted molecules reside as guests. The host material may be a hole transporting matrix selected from substituted triarylamines. An example of a host material is 4,4'-N,N'-dicarbazole-biphenyl (CBP), which has the general formula

The emissive layer also contains polarizing molecules, is present as a dopant in the host material and has a dipole moment, and when the emissive dopant molecules emit light, affects the wavelength of the emitted light.

A layer formed of an electron transport substance is used to transport electrons into the emissive layer comprising the emissive molecule and the optional host material. The electron transport material may be an electron transport matrix selected from metal quinoxaline salts, oxidazoles and triazoles. An example of an electron-transporting substance is tris-(8-quinolinolato)aluminum (Alq ₃ ).

A layer formed of a hole transport substance is used to transport holes into the emissive layer comprising the emissive molecule and the optional host material. An example of a hole transporting substance is 4,4-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl ["α-NPD"].

The use of an exciton-blocking layer ("blocker") to confine the excitons in the light-emitting layer ("light-emitting region") is highly preferred. For hole transport hosts, a blocking layer can be placed between the light emitting layer and the electron transport layer. An example of such a barrier material is 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (also known as bathocuproine or BCP), which has the general formula

IV. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1. Proposed energy transfer mechanism in a multilevel system. Ideally, when the triplet state in the fluorochrome undergoes non-radiative recombination, all excitons are transferred to the singlet state of the fluorochrome. Forster transmission is represented by straight lines and Dexter transmission by dashed lines. Electron-hole recombination generates singlet and triplet excitons in the host material. These excitons are then transferred to a phosphorescent sensitizer. The probability of direct transfer into fluorescent dyes by Forster to singlet state or Dexter to triplet state is low. This latter mechanism is the source of loss and it is represented by a "cross" in the figure. The singlet excitons in the phosphor then undergo an intersystem transition (ISC) and transfer to the triplet state. From this state, the triplet can undergo dipole-dipole coupling with the singlet state of the fluorescent dye, or in another loss mechanism, they can be Dexter transferred to the triplet state. It should also be pointed out that electron-hole recombination is also possible for phosphors and fluorescent dyes. The direct formation of the triplet state on the fluorochrome is an additional loss. Inset. Structure of the electroluminescent device fabricated in this study. Multiple doped layers close to the mixed layer of CBP: 10% Ir(ppy) ₃ : 1% DCM2. Two variants are also manufactured. Second device: Ir(ppy) ₃ was exchanged with Alq ₃ to check whether the intermediate stage was fluorescent and not phosphorescent. Third Device: Separately, a device with an emissive layer containing CBP:1% DCM2 was fabricated and direct transfer between CBP and DCM2 was examined.

Figure 2. External quantum efficiency of DCM2 emission in three devices. The sensitization of Ir(ppy) ₃ significantly improves this efficiency. It was also noted that the presence of Alq ₃ made little difference in all the fluorescent devices.

Figure 3. In the spectra of three devices, characteristic peaks were observed: CBP (λ-400nm), TPD (λ-420nm), Alq ₃ (λ-490nm), Ir(ppy) ₃ (λ-400nm) and DCM2 (λ-590nm). About 80% of photons in Ir(ppy) ₃ devices are emitted by DCM2. All spectra were recorded at a current density of ~1 mA/ ^cm2 .

Figure 4. Transient response of DCM2 and Ir(ppy) ₃ components in CBP:10%Ir(ppy) ₃ :1%DCM2 devices. The instantaneous lifetime of DCM2 is ~1 nanosecond (ns), so for the case of energy transfer from Ir(ppy) ₃ , the response of DCM2 should be determined by the instantaneous lifetime of Ir(ppy) ₃ . In this initial 100 ns wide electrical excitation pulse, this is clearly the case for energy transfer from the triplet state in Ir(ppy) ₃ to the singlet state in DCM2. During the excitation pulse, however, singlet transfer to DCM2 was observed, resulting in "ripples" in the transient response. These ripples result from fluctuations in current density and discharge of traps on the falling edges of the pulses. It must be noted that the trends in the DCM2 and Ir(ppy) ₃ transient responses ended up diverging slightly. This is attributed to the recombination and luminescence of a small amount of charges trapped on the DCM2 molecule.

Figure 5. Schematic of a device with an interlayer of ISC agents between the ETL and HTL.

Figure 6. IV characteristics of the device described in Example 5/Figure 5.

V. Detailed Description of the Invention

The present invention relates to organic light emitting devices (OLEDs) consisting of an emissive layer containing an organic compound as an emitter and individual intersystem transition ("ISC") molecules for enhancing emission efficiency. Embodiments are described that enhance the emission efficiency of fluorescent and phosphorescent emitters.

It is preferred that there is sufficient spectral overlap between the ISC molecule and the emissive molecule. One way to measure spectral overlap is by integrating the absorption and emission spectral regions over a range of energies (wavenumbers) where the two spectral regions have non-zero values. This approach is similar to that in A.Shoustikov, Y.You, and M.E.Thompson, "Electroluminescence ColorTuning by Dye Doping in Organic Light Emitting Diodes", Quantum Electronics Relevant in the manner taken in Equation 2(a) of IEEE Journal of Monographs 1998, 4, 3-14. One way is to normalize the absorption and emission spectra to its integrated intensity. The product of the spectrum normalized in the energy range where the two spectral regions have non-zero values is integrated. This range is taken as 180 nm to 1.5 micron wavelength. If the value is at least 0.01, and more preferably at least 0.05, there is sufficient spectral overlap.

It is also preferred that there is sufficient spectral overlap between the emission spectrum of the host material and the absorption spectrum of the ISC agent. The product of the spectrum normalized in the energy range where the two spectral bins have non-zero values is integrated. This range is taken as 180 nm to 1.5 micron wavelength. If the value is at least 0.01, and more preferably at least 0.05, there is sufficient spectral overlap.

The present invention will now be described in detail with respect to certain preferred embodiments of the invention. It should be understood that these embodiments are examples for illustrative purposes only, and the invention is not limited thereto.

V.A. Use of ISC agents that enhance fluorescence emission

V.A.1. Overview of the First Embodiment

Embodiments of the present invention generally relate to a phosphorescent sensitizer for a fluorescence emitting molecule that emits light when a voltage is applied along a hybrid structure of an organic light emitting device, the sensitizer being selected from phosphorescent organometallic complexes , as well as some structures involved in optimizing the emission of light-emitting devices and related molecules of these structures. The term "organometallic" is generally as understood by those skilled in the art, for example in "Inorganic Chemistry" (Second Edition), Gary L. Miessler and Donald A. Tarr, Prentice-Hall (1998) the definition given. The invention further relates to a sensitizer in the emitting layer of an organic light-emitting device, the sensitizer molecule consisting of a phosphorescent cyclometalated iridium complex. A discussion of the chromatic form of color, including a description of the CIE regulations, is found in H.Zollinger.Color Chemistry, VCH Press, 1991 and H.J.A.Dartnall, J.K.Bowmaker. and J.D.Mollon, Proc.Roy.Soc.B (London), 1983, 220, 115-130.

V.A.2. Example of the first embodiment

The structures of the organic light emitting devices of Examples 1, 2 and 3 are shown in the inset of FIG. 1 .

Example 1

Organic layers were deposited on clean glass substrates previously coated with a 1400 Angstrom thick coating of transparent and conductive indium tin oxide by high vacuum (10 ^-6 Torr) thermal evaporation. 600 angstrom thick layer of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1-biphenyl]-4,4-diamine ["TPD"] for transporting holes to the light-emitting layer. The light-emitting layer consisted of an alternating series of 10 Å thick layers of CBP doped to 10% by mass of Ir(ppy) ₃ and 10 Å thick layers of CBP doped to 1% by mass of DCM2. A total of 10 doped layers were gathered with a total thickness of 100 Angstroms. Excitons are confined in the light-emitting region by a 200-angstrom thick layer of the exciton-blocking substance 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (also known as bathocuproine or BCP) . A 300 Angstrom thick layer of the electron transport substance tris-(8-quinolinolato)aluminum (" _Alq3 ") was used to transport electrons to the light emitting region and reduce absorption at the cathode. A mask with 1 mm diameter openings was used to define a cathode consisting of a 1000 Angstrom thick layer of 25:1 Mg:Ag, with a 500 Angstrom thick capping layer. Compound Ir(ppy) ₃ [sensitizer/ISC agent in Example 1] has the following structural formula:

Comparative Example 2

As a control, the same device as in Example 1 was fabricated except that Ir(ppy) ₃ was replaced by _Alq3 , which had similar emission and absorption spectra but no observable phosphorescence at room temperature.

Comparative Example 3

As a second control, the same device as in Example 1 was fabricated except that the intermediate energy transfer step for detecting direct energy transfer from CBP to DCM2 was omitted.

Results of Examples 1, 2 and 3

The external quantum efficiency (photons per electron) for each example is given in FIG. 2 as a function of injected current for the DCM2 portion of the emission spectrum. The DCM2 emission efficiency of devices containing phosphorescent sensitizers is significantly higher than that of its fluorescent analogues. In fact, the peak efficiency of (3.3±0.1)% is significantly higher than the best result of ~2% observed for DCM2 in a previous study (CH Chen, CW Tang, J. Shi, and KP Klubeck, "Optimum "Improved red dopants for organicluminescent devices", Macromolecular Symposia, 1997, 125, 49-58)). This demonstrates that in Example 1, the host triplet state is transferred to the fluorescent singlet state. As a more quantitative comparison of the increase in emission caused by the sensitizer, the inventors noted a difference in the quantum efficiency of the DCM2 emission, which is highest in this example without the phosphorescent sensitizer The efficiency is 0.9±0.1% and 3.3% in this example with phosphorescent sensitizer [see FIG. 2 and the addition of _Alq3 in the CBP:DCM2 device in comparative example 2. ]. The ratio of the efficiency of sensitized to unsensitized devices is 3.7 ± 0.4, which corresponds to the range between (singlet + triplet) to (singlet only) [i.e. (1+3)/(1+0)] emissions are very close to the expected value of four (4).

The emission spectra of the OLEDs of the three examples are given in FIG. 3 . All devices showed energy transfer to the fluorescent dye. By taking the area under each spectral peak, the inventors found that about 80% of the photons were emitted by DCM2 in devices containing the Ir(ppy) ₃ sensitizer. The remainder is attributed to CBP emission at ~400nm, TPD emission at ~420nm and Ir(ppy) ₃ emission at ~500nm. In devices doped with 10% Alq ₃ , an emission peak was observed at ~490 nm. This is consistent with the observation of _Alq emission in a non-polar host (CBP). (V. Bulovic, R. Deshpande, METhompson, and S R Forrest, "Tuning the color emission of thin film molecular organic light emitting devices by the solid state solvation effect", Chemical Physics Letters (1999).

Confirmation of the energy transfer process in Eq. 2 is shown in Fig. 4, which illustrates the transient nature of the DCM2 and Ir(ppy) components of the emission spectrum. These data were obtained by applying ~100 ns electrical pulses to the electroluminescent device. The obtained emissions were measured with an ultra-high-speed scanning camera. If part of the DCM2 emission is generated by (energy) transfer from the Ir(ppy) ₃ triplet state (Eq. 2), the proposed energy transfer must result in delayed DCM2 fluorescence. Moreover, since the radiation lifetime of DCM2 is much shorter than that of Ir(ppy) ₃ , the transient decay of DCM2 should match that of Ir(ppy) ₃ . After the initial peak, the DCM2 decay actually follows the Ir(ppy) ₃ decay, most likely due to singlet-singlet transition (Eq. 2). The transient lifetime of Ir(ppy) ₃ in this system is ~100 ns, in contrast to ~500 ns without DCM2, demonstrating ~80% energy transfer. The shortening of the triplet lifetime due to energy transfer to the fluorescent acceptor is desirable. Not only does it improve the transient response of the system, but it also shows that the probability of triplet-triplet annihilation is inversely proportional to the square of the triplet lifetime. (MA Baldo, ME Thompson, and SR Forrest, "An Analytical Model of Triplet-Triple Annihilation in Electroluminescent Phosphorescent Devices" (1999)). Therefore, it can be expected that this multilevel energy transfer will reduce the quenching of the triplet state, thereby further enhancing the potential of high-efficiency sensitized fluorescence.

These three examples illustrate general techniques for improving fluorescence efficiency in guest-host organismal systems. Further improvement can be expected by mixing the host, phosphorescent sensitizer and fluorescent dye, rather than doping in the same thin layer as in this study, although the thin layer approach suppresses the transfer of triplet states from the host to the fluorophore. Direct Dexter transfer of , they will be attrition in the process. In order to further reduce the loss in multilevel energy transfer, the ideal system can add low concentration of sterically hindered dyes. For example, the introduction of a spacer group into the DCM2 molecule should reduce the probability of Dexter transfer to the dye while at the same time minimally affecting its participation in Forster transfer or its luminescence efficiency. Since Dexter transfer can be understood as the simultaneous transfer of electrons and holes, steric hindrance can also reduce the possibility of charges being trapped on fluorescent dyes. Similar efforts have been made to reduce the formation of non-radiative excimers in the DCM2 variant [Chen, Tang, Shi, and Klubeck, "Improved red dopants for organic EL Devices", vol. Molecular Papers, 1997, 125, 49-58]. At the same time, the optimization of the device structure will reduce the Ir(ppy) ₃ emission to a lower level.

V.B. Use of ISC Agents to Enhance Phosphorescence Emission

V.B.1. Overview of the second embodiment

A second embodiment concerns the case where the emissive molecule is phosphorescent and the use of intersystem transition molecules enhances the efficiency of phosphorescent emission.

V.B.2. Example of the second embodiment

Prophetic Example 4

OLEDs were fabricated with a conventional diamine hole transporter and an electron transport layer (ETL) consisting of three different substances. The ETL is roughly 80% conventional electron transport material (such as Zrq4), 15% intersystem transition agent (such as diphenyl ketone; other ISC agents can be found in the literature of Gilbert and Baggott) and 5% phosphorescent emission body (such as PtOEP, platinum octaethylporphyrin). An ISC agent is chosen such that its absorption spectrum strongly overlaps the fluorescence spectrum of the ETL. Hole-electron recombination occurs at or near the HTL/ETL interface, generating a mixture of singlet and triplet excitons. The singlet excitons on the ETL efficiently transfer their energy to the ISC agent, through the n→π ^* state or some other suitable process, they will efficiently intersystem transition to their triplet state.

The triplet energy of the ISC agent is then transferred into the dopant and emitted on the phosphorescent dopant. The triplet excitons formed on the ETL will transfer directly to the dopant or energy transfer to the ISC agent and then transfer energy to the dopant. The ISC agents in this application are specified to completely quench singlet excitons, achieving good yields for transfer of triplet excitons to phosphorescent dopants.

The chemical formula of Zrq ₄ is

Use of transition agent between V.C. systems as filter and conversion agent

V.C.1. Overview of the Third Embodiment

In a third embodiment of the invention, a thin layer of ISC agent is placed between the HTL and the ETL. The ISC agent is chosen such that the optical absorption spectrum of the ISC agent strongly overlaps the emission line of the species found at the site of recombination.

In the control experiments discussed below, the inventors used 2,7-diphenylfluorenone ("ISC-F") as the ISC agent. ISC agents suitable for example filter/conversion agents can be selected from acridine, acridone, brominated polycyclic aromatic hydrocarbon compound, anthraquinone, α-β-diketone, phenazine, benzoquinone, diacetyl, rich fullerene, thiophene, pyrazine, quinoxaline, and thianthrene.

V.C.2. Example of the third embodiment

Example 5

In Figures 5 and 6, the inventors present control experiments for devices without phosphorescent dopant emitters. Examples of the third embodiment can have phosphorescent emitters in the ETL layer.

The structure of the device of this embodiment is schematically given in FIG. 5 . It consists of a structure with α-NPD/ISC-F/Alq ₃ . (Alq ₃ layer is not doped). The IV characteristics of the device are given in Fig. 6. Here, the device area is 3.14 mm ² . The key point is that there is no light at low to medium bias. This result suggests that the ISC filter/shifter certainly quenches the singlet state. [At very high displacements (>17 volts), a weak green light emission was observed. The spectrum of this output indicated that it was from Alq ₃ . To explain the emission, at high displacements there is electron leakage to Alq ₃ or ISC-F transfers energy back to the singlet state in Alq ₃ . ]

In the device for the third embodiment of the invention, the Alq ₃ region is doped with a phosphorescent emitter. The inventors were able to know that triplet excitons had been efficiently injected into the Alq ₃ layer due to the phosphorescent emission induced by the doped emitter.

In contemplated embodiments of the invention, 2,7-diphenylfluorenone ("ISC-F") transports electrons to the α-NPD/ISC-F interface. Hole/electron recombination at or near this interface will simultaneously yield singlet and triplet excitons. These two kinds of excitons are easily transferred into the ISC-F layer. Any singlet state transferred into (formed in) the ISC-F layer will rapidly intersystem transition to the triplet state. Thus, all excitons present will be efficiently transferred to the triplet state within the device.

Specifically, the triplet excitons will diffuse through the ISC-F layer and transfer to the Alq ₃ layer. Transferring to Alq ₃ made easy. Although the triplet energy of Alq ₃ is not known exactly, it is believed to be between 550 and 600 nanometers. This accurately and efficiently traps triplet excitons from ISC-F in the right region. Using the ISC agent in this way, the inventors can prevent singlet excitons from ever reaching the emitting region of the device. By doping the emissive region with a phosphorescent dye, the inventors efficiently extracted energy luminescently. The ISC agent is used here as a filter, allowing only triplet excitons to be injected into the Alq ₃ layer. The requirement for such an ISC filter/conversion agent is that it has both singlet and triplet energies lower than the energy of the species at or near the recombination site (in this example α-NPD), and the Has a triplet energy higher than the emission region (it must not be at the recombination site, Alq ₃ in this example). The substance must have a high ISC efficiency.

V.D. Other Discussions

V.D.1. Spectral Overlap

In an embodiment of the invention there should be spectral overlap between the emissive molecule and the intersystem transition molecule. The nature of the overlap depends on the use of the device, which includes large displays, vehicles, computers, televisions, printers, large walls, theater or stadium displays, billboards and signage. For display applications of the devices of the invention there should be spectral overlap in the visible spectral region. For other applications, such as the use of this device in printing, the emission spectrum does not need to overlap with the artificial daylight photopic response.

V.D.2. Other examples of sensitizers/ISC agents of the first embodiment

芳族结构可具有烷基取代基或对芳族结构的原子加以改变。 Examples of the invention that enhance fluorescence emission are not limited to the sensitizer molecules of this embodiment. Consider using metal complexes in which there is sufficient spin-orbit coupling to permit radiative relaxation of the process. Among the ligands, one of ordinary skill in the art can modify the organic components of Ir(ppy) ₃ (given directly below) to obtain the desired properties.

The aromatic structure may have alkyl substituents or changes to the atoms of the aromatic structure.

These molecules related to Ir(ppy) ₃ can be formed from commercially available ligands. The R group can be an alkyl or aryl group and is preferably in the 3, 4, 7 and/or 8 position of the ligand (for steric reasons).

Other possible sensitizers are listed below:

This molecule is expected to have a blue-shifted emission compared to Ir(ppy) ₃ . R and R' can independently be alkyl or aryl.

Organometallic compounds of osmium are useful in the present invention. Examples are the following.

These osmium complexes are octahedral with 6d electrons (isoelectronic to the Ir analogs) and have good intersystem transition efficiencies. R and R' are independently selected from alkyl and aryl. It is believed that they have not been reported in the literature.

Here X can be selected from N or P, and R and R' are independently selected from alkyl and aryl.

V.D.3. Other molecular descriptions

The molecules of the hole transport layer of the present invention are described below.

The present invention can be used in the hole-transport layer of OLEDs together with other hole-transport molecules known to the skilled person.

Molecules used as host materials in the emissive layer of the present invention are described below.

The present invention can be used as a host material for the emissive layer of an OLED together with other molecules known to the skilled person. For example, the host material may be a hole transporting matrix and be selected from substituted triarylamines and polyvinylcarbazoles.

Molecules used as the exciton-trapping layer of Example 1 are described below. The present invention can be used with other molecules for the exciton-capping layer, provided they meet the requirements given here.

V.D.4. Purpose of device

The OLEDs of the invention can be used in essentially any type of device consisting of OLEDs, for example for incorporation into large displays, media, computers, televisions, printers, large walls, theater or stadium displays, billboards or signage Among the OLED series in the brand.

The invention disclosed here can be used in conjunction with several pending patent applications: "High Reliability, High Efficiency, Integratable Organic Light Emitting Devices and Methods of Produeing Same)", serial number No.08/774,119 (applied on December 23, 1996); "Novel Materials for Multicolor Light Emitting Diodes)", serial number No.08/850,264 (on May 1997 Application filed on 2nd); "Electron Transporting and Light Emitting Layers Based on Organic Free Radicais" (Electron Transporting and Light Emitting Layers Based on Organic Free Radicais)", serial number No.08/774,120 (December 23, 1996); "Multiple Multicolor Display Devices (Multicolor DisplayDevices)", serial number No.08/772.333 (applied on December 23, 1996); "Red-Emitting Organic Light Emitting Devices (OLED)"; serial number No. 08/774,087 (filed on December 23, 1996); "Driving Circuit For Stacked Organic Light Emitting Devices (Driving Circuit For Stacked Organic Light Emitting Devices)", Serial No. 08/792,050 (filed on February 3, 1997 Japan application); "High Efficiency Organic Light Emitting Device Structures (High Efficiency Organic Light Emitting Device Structures)", serial number No.08/772,332 (applied on December 23, 1996); "Vacuum-deposited, non-polymeric flexible organic Vacuum Deposited, Non-Polymeric Flexible Organic Light Emitting Devices", Serial No. 08/789,319 (applied January 23, 1997); "Displays Having Mesa Pixel Configuration", Serial No. 08/794,595 (applied on February 3, 1997); "Stacked Organic Light Emitting Devices (Stacked Organic Light Emitting Devices)", Serial No. 08/792,046 (applied on February 3, 1997); "High Contrast Transparent Organic Light Emitting Devices (High Contrast Transparent Organic Light Emitting Devices)", serial number No.08/792,046 (applied on February 3, 1997); "High Contrast Transparent Organic Light Emitting Device Display (High Contrast Transparent Organic Light Emitting Device Display)", Serial No.08/821,380 (applied on March 20, 1997); "Organic Light Emitting Devices Containing A Metal Complex of 5-Hydroxy- Quinoxaline as A Host Material), serial number No.08/838,099 (applied on April 15, 1997); "Light Emitting Devices Having High Brightness (Light Emitting Devices Having High Brightness)", serial number No. filed on April 18); "Organic Semiconductor Laser", Serial No. 08/859,468 (applied on May 19, 1997); "Saturated Full Color Stacked Organic Light-Emitting Devices (Saturated Full Color Stacked Organic Light Emitting Devices), Serial No. 08/858,994 (applied May 20, 1997); "Plasma Treatment of Conductive Layers", PCT/U597/10252, (June 1997 12); "Novel Materials for Multicolor Light Emitting Diodes (Novel Materials for Multicolor Light Emitting Diodes)", serial number No.08/814,976, (applied on March 11, 1997); "Novel Materials for Multicolor Light Emitting Diodes ( Novel Materials for Multicolor Light Emitting Diodes)", serial number No.08/771,815, (applied on December 23, 1996); "Patterning of ThinFilms for the Fabrication of Organic Multi-color Displays), PCT/US97/10289, (applied on June 12, 1997), and "Double Heterostructure Infrared and Vertical Cavity Surface Emitting Organic Lasers", Attorney Docket No. 10020/35 (filed July 18, 1997), each of the pending applications is incorporated herein by reference in its entirety.

Claims (19)

1. An organic light-emitting device comprising a hybrid structure for emitting light, comprising an emissive layer, Wherein the emissive layer is a combination of a host material and an emissive molecule present as a dopant in the host material: wherein the emissive molecule emits light when a voltage is applied along the hybrid structure; and Wherein the hybrid structure includes an intersystem transition molecule, so that emission efficiency is enhanced by using the intersystem transition molecule. 2. The organic light emitting device of claim 1, wherein the emission spectrum of the intersystem transition molecule substantially overlaps the absorption spectrum of the emissive molecule. 3. An organic light-emitting device comprising a hybrid structure for emitting light, comprising an emissive layer, Wherein the emissive layer is a combination of a conductive host material and a fluorescent molecule present as a dopant in the host material: wherein the emissive molecule emits light when a voltage is applied along the hybrid structure; and The hybrid structure here includes an intersystem transition molecule belonging to a high-efficiency phosphor, the emission spectrum of which substantially overlaps the absorption spectrum of the emissive molecule. 4. The emissive layer of claim 3, wherein the intersystem transition molecule is Ir(ppy) ₃ . 5. The device of claim 3, wherein the fluorescent molecule is DCM2. 6. The device of claim 1, wherein the emissive molecule is phosphorescent. 7. The device of claim 2, wherein the emissive molecule is phosphorescent. 8. The device of claim 6, wherein the emissive molecule is PtOEP. 9. The device of claim 1, wherein there is a thin layer comprising an intersystem transition agent, wherein the thin layer is disposed between the hole transport layer and the electron transport layer. 10. The device of claim 2, wherein the emissive molecule is phosphorescent and wherein the thin layer comprising the intersystem transition agent suppresses emission from the singlet state. 11. The device of claim 2, wherein the emissive molecule is phosphorescent and wherein a thin layer including an intersystem transition agent enhances triplet emission. 12. An organic light-emitting device comprising a hybrid structure for emitting light, comprising: comprising an emissive layer of host material; and Emissive molecules, present as dopants in the host material, emit light when a voltage is applied along the sides of the hybrid structure; hole transport layer; electron transport layer; and An intersystem transition agent wherein there is sufficient spectral overlap between the emission spectrum of the intersystem transition agent and the absorption spectrum of the emissive molecule. 13. The device of claim 12, wherein emission efficiency is increased relative to a device having emissive molecules but no intersystem transition agent. 14. The device of claim 12 having an exciton-confinement layer. 15. The device of claim 14, wherein the exciton-blocking layer comprises 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline. 16. The device of claim 12, wherein the emissive molecule is fluorescent and the intersystem transition agent is an organometallic compound comprising a metal of the third row of the periodic table. 17. The device of claim 12, wherein the emissive molecule is phosphorescent. 18. The device of claim 12, wherein the emissive molecule is phosphorescent and the intersystem transition agent suppresses emission from the singlet state. 19. The organic light-emitting device according to claim 1, which is used in large-scale displays, vehicles, computers, televisions, printers, large-area walls, theater or stadium display screens, billboards and signal boards.

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